## Let $R(a, b, c)$ be the maximum area covered by three non-overlapping circles inside a triangle with edge lengths $a$, $b$ and $c$.

Let $S(n)$ be the average value of $R(a, b, c)$ over all integer triplets $(a, b, c)$ such that $1 \le a \le b \le c \lt a + b \le n$.

You are given $S(2) = R(1, 1, 1) \approx 0.31998$, $S(5) \approx 1.25899$.

Find $S(1803)$ rounded to $5$ decimal places behind the decimal point.

### To solve the given problem, we need to calculate the value of $D(10^9, 10^5, 10^5)$ using the given formulas.

We can start by implementing a function to check if a number is prime:

“`python

def is_prime(n):

if n < 2:
return False
for i in range(2, int(n ** 0.5) + 1):
if n % i == 0:
return False
return True
```
Next, we can implement the function $d(p, n, k)$:
```python
def dpnk(p, n, k):
if k == 0:
return 1
return sum(dpnk(p, i, k - 1) for i in range(1, n + 1)) % p
```
Then, we can implement the function $D(a, b, k)$:
```python
def Dak(a, b, k):
primes = [p for p in range(a, a + b) if is_prime(p)]
return sum(dpnk(p, p - 1, k) % p for p in primes)
```
Finally, we can calculate the value of $D(10^9, 10^5, 10^5)$:
```python
result = Dak(10**9, 10**5, 10**5)
print(result)
```
When running this code, it will output the value of $D(10^9, 10^5, 10^5)$.
Note: Since the given problem involves large numbers, the calculations may take a long time to execute. Consider using an optimized approach or utilizing parallel processing techniques for better performance.

##### More Answers:

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